Time is expensive. So, you can find parts elsewhere for much less, but it can take a while to find an equivalent option setup for prototyping. It's not as much

Time is expensive. So, you can find parts elsewhere for much less, but it can take a while to find an equivalent option setup for prototyping. It's not as much of an issue if you've got a stack of blank SMD breakout boards. If you're doing some DIY work and you can find out someone's already designed a module that fits your needs, then why not. Consider the DC motor/stepper feather for example. Perhaps it's $8 worth of components if you're sourcing things piece by piece. Paying a ~$10 premium when you're making a one-off design seems entirely reasonable compared to trying to design a board yourself, waiting for the PCB fab, etc. I'm an EE and I source plenty from digikey/mouser/etc for personal projects. There's a gap for the occasional prebuilt board, break out board, or oddball electromechanical part (which can be a pain to find at other suppliers). Higher cost distributors like adafruit/sparkfun do have their place even when you have the background.